A spun-bond apparatus generally comprises a spinneret from which a curtain of thermoplastified filaments emerge at a temperature equal to or above the melt temperature of the thermoplastic synthetic resin, a cooling unit below the spinneret for quenching the thermoplastified synthetic resin, a discharge gap through which the filaments are entrained, at least in part by the cooling air, and an intermediate passage between the cooling device and the discharge gap through which the filament curtain is guided, the filaments being stretched along the path from the spinneret to a collecting belt below the discharge gap at which the mat, fleece or jumble of filaments from the gap can be collected in a continuous web. Below the collecting belt, which is air-permeable, the region at which the web collects can be evacuated.
The cooling air passes via the intermediate passage into the discharge gap and impinges upon the collecting belt together with the filaments.
The discharge gap can, in vertical section, have the configuration of a venturi nozzle, with a convergence toward a constriction and possibly a divergence after the constriction. Preferably the gap is a parallel gap, i.e. a gap defined between two generally parallel walls.
In some known spun-bond apparatuses, the filament speeds attain values of 1000 m/min to 2500 m/min depending upon the configuration and arrangement of these structures.